1. Field of the Invention
This invention relates to sensors, in particular position and speed sensors. Position sensors provide signals indicative of the position of a moving member with which they are associated relative to some fixed datum and, by appropriate processing of the position signals, further signals indicative of the speed of movement of the moving member relative to this datum may also be derived. Speed sensing systems serving this latter purpose form a further subject of the present invention.
The invention also relates to sensors for use with electrical machines, such as, inter alia, brushless d.c. drives and synchronous motors. Machines and drives of these kinds are used in machine tool positioning and robots, and in addition to these applications, angle sensing in general and motor commutation represent further favoured fields of use. Position and speed sensors according to the present invention and drive systems incorporating them are also suited to use with saturable variable reluctance machines and drive systems such as those forming the subjects of co-pending patent applications entitled "Variable Speed Variable Reluctance Electrical Machines" and "Control Systems for Variable Reluctance Electrical Machines", respectively Ser. No. 789,038 now U.S. Pat. No. 4,670,696, issued June 2, 1987, and Ser. No. 788,856.
2. Description of the Prior Art
Known position and speed sensors include absolute and incremental digital encoders, resolvers based on the varying mutual inductances of windings moved relative to one another, variable-capacitance devices, Hall devices sensing permanent-magnet fields, and inductosyn type transducers.
For some applications, these solutions for position and speed sensing may be too costly, insufficiently robust, or unreliable in hostile environments, or they may have insufficient resolution. Some do not lend themselves to the derivation of an acceptable speed signal.